Gradients in the composition of reservoir fluids are now routinely analyzed to evaluate petroleum reservoirs. Analysis may involve fitting compositions measured at multiple locations to equations of state. Such equations of state that are used include the Peng-Robinson or the Flory-Huggins-Zuo equations of state. These equations are complex and involve multiple fitting parameters, and the application of these involves time-consuming processes such as tuning. As a result, interpretation using these equations occurs after the logging job is complete and the logging tool removed from the well, so real-time application is not possible.
Currently, there are no simplified equations of state that may be interpreted in real time without tuning for analysis of petroleum reservoir data.